1. Field of the Invention
This invention relates generally to downhole tools for use in oil or gas wells and, more particularly, to wellbore annulus pressure-responsive tools which are actuated by an electrically controlled device.
2. Background of the Art
A variety of downhole devices (tools) are utilized in wellbores to facilitate production of hydrocarbons from subterranean formations. For example, packers are commonly utilized to seal an annulus between the packer and a tubular member (typically a wellbore casing) placed within the wellbore. Producing wellbores usually contain formation fluids, such as hydrocarbons (oil and or gas) and/or connate water. During drilling operations, wellbores typically contain drilling fluids (commonly known as the "drilling mud" or "mud") pumped into the wellbore from a surface location. The pressure at a given depth in the wellbore depends upon the weight of the fluid column above the depth point. Such a pressure is referred to as the hydrostatic pressure or simply the hydrostatic, and it may vary between a few hundred psi to several thousand psi.
A variety of downhole tools utilize the hydrostatic pressure to perform a useful function. The majority of such tools utilize either a mechanical force or an explosive charge to actuate a device, which in turn enables the hydrostatic pressure to act upon a secondary devices to perform an operation downhole. More recently, electrically operated devices have been utilized in commercial tools to selectively allow the application of the hydrostatic pressure to perform a specific function.
For example, U.S. Pat. No. 5,251,703 to Skinner discloses a system wherein a solenoid valve in a normally closed position is placed between the well annulus and a chamber. The chamber has two sections separated by a power piston. One section communicates with the wellbore via the solenoid valve and the other section is filled with a working liquid and compressed nitrogen to provide back pressure to the first section. When the solenoid valve is opened, hydrostatic pressure is applied to the first section, causing the piston to move, which operated a device coupled thereto. U.S. Pat. No. 5,251,703 to Skinner discloses three chambers and a plurality of electrically-operated valves for manipulating the application of the hydrostatic pressure to a piston in one of the chambers to cause a device to operate.
U.S. Pat. No. 5,240,077 to Whitsitt discloses a hydraulic setting tool, which is actuated by an electric motor driving a pump. The Whitsitt device uses a closed hydraulic system to maintain a minimum head pressure of hydraulic fluid at the pump intake to reduce or eliminate cavitation, thus improving the tool viability in high temperature wells.
The present invention provides a relatively simple and reliable downhole tool wherein the hydrostatic pressure is applied to at least one atmospheric chamber in the tool by activating a remotely controlled electrically-operated device. A control circuit in the tool activates the device in response to a coded signal transmitted from a remote location, such as the surface.